Traditionally, silicone formulations rely on physical means, this being mainly a factor of modulus of elasticity and surface tension to create a low fouling surface. The traditional polydimethylsiloxane (PDMS) coatings have shown difficulty in resisting slime fouling over time, thus decreasing the advantage of drag reduction.
Hence, there is a need for fouling control polysiloxane-based coating compositions combining the benefits of conventional polysiloxane-based fouling-release coating compositions with the benefits of biocide-based antifouling coating compositions.
WO 2007/053163 discloses an antifouling material that may include one or more of a number of suitable copolymers (e.g. block copolymers, graft copolymers, etc.) which provide biocidal and/or fouling release characteristics. The copolymers may include a polysiloxane backbone with one or more polymers grafted onto the polysiloxane backbone. Such grafted polymers may carry biocidal groups.
WO 2008/132195 discloses an antifouling coating composition comprising a curable polymer (e.g. an organosiloxane-containing polymer) and an organosilicone polymer.
WO 2008/132196 discloses a method to physically deter marine fouling which method involves forming on the substrate a coating composition comprising curable polyorganosiloxane, polyoxyalkylene block copolymer, organosilicon cross-linking agent and/or catalyst. The polyoxyalkylene is reacted to the silicone binder by addition reaction (vinyl/hydrid) to form a block copolymer of polyoxyalkylene and polysiloxane. The copolymer can subsequently be terminated with vinyltrimethoxysilane to form a moisture curable binder.
US 2004/006190 discloses a room-temperature curable organopolysiloxane composition, which includes (A) an organopolysiloxane with the terminals blocked with a hydroxyl group, a hydrolysable group, or both these types of groups, and (B) an organosilicon compound containing a hydrolysable group, a partial hydrolysis-condensation product thereof, or a mixture of the two, and (C) a polysiloxane with at least one oxyalkylene group bonded to a silicon atom via, for example, a C—C—Si linkage.
WO 2002/088043 discloses a process for coating a siliceous substrate with a silicon-containing layer, wherein in a first step a layer comprising a biocide is applied.
US 2002/0197490 A1 discloses a curable antifouling polysiloxane based composition comprising hydrophobic silica possibly in combination with hydrophilic silica. In some embodiments, the composition further comprises a silicone oil, e.g. oils comprising polyethylene glycol or polypropylene glycol moieties. It is further envisaged, that antifouling agents may be used, in particular copper and inorganic copper compounds.
EP 2 103 655 A1 discloses a curable antifouling polysiloxane based composition comprising a reaction curable silicone rubber and a particularly designed organopolysiloxane mixture. In some embodiments, the composition further comprises a silicone oil, e.g. a polyether-modified silicone oil. It is further envisaged, that antifouling agents may be used, in particular copper and inorganic copper compounds.
U.S. Pat. No. 6,313,193 B1 i.a. discloses a composition comprising a silanol-terminated polydimethyl siloxane, a dimethylethoxy-terminated polydimethyl siloxane, polydiethoxy siloxane, and benzalkonium chloride. The polydiethoxy siloxane reacts with the polydimethyl siloxanes so that the polydiethoxy siloxane becomes an integral part of the binder network.
JP 2006 052283 A discloses a coating composition comprising a polyether-modified silicone oil having polyoxyalkylene side chains, an acrylic type binder system based on a polysiloxane macropolymer and an antifoulant.
JP 2006 299132 A discloses an antifouling coating composition which is based on a vinyl copolymer binder system which include polysiloxane side chains, and which is modified with certain reactive silanes, and which further comprises, e.g., an poly(oxyalkylene)-modified polysiloxane. The composition may also include an antifouling agent.
The silicone based fouling release coatings have demonstrated an advantage over conventional antifouling coatings showing significant lower drag resistance, hence reduced fuel consumption of marine vessels. The difference is especially obvious as long as the silicone coating is free from marine fouling including slime fouling. Many conventional silicone coatings have until now only been able to maintain a slime free surface for a shorter period.
Some traditional biocide containing antifouling coatings have demonstrated a greater resistance towards marine fouling compared to the silicone based fouling release coatings under, e.g., static conditions. The surface characteristics of such a coating will however lead to an increased drag resistance compared to silicone coatings even when the surface is fouling free.
The rationale behind the present invention has been to prolong the slime free period of a silicone based coating by combining the biocidal components from the antifouling coatings with a silicone based fouling release coating. This provides a coating with low drag resistance that will remain fouling free for a longer time than conventional silicone based fouling release coatings.